1. Field of the Invention
The present invention relates to a carrier film for mounting a polishing workpiece and a method for making the same, and more particularly, to a carrier film for mounting a polishing workpiece and a method for making the same which are used in the chemical mechanical polishing (CMP) process.
2. Description of the Related Art
Polishing generally refers to a wear control for a preliminary coarse surface in the process of chemical mechanical polishing, which makes the slurry containing fine particles evenly dispersed on the upper surface of a polishing pad, and at the same time places a polishing workpiece against the polishing pad and then rubs the polishing workpiece repeatedly with a regular motion. The polishing workpiece may be objects such as a semiconductor, a storage medium substrate, an integrated circuit, an LCD flat-panel glass, an optical glass and a photoelectric panel. During the polishing process, a carrier film must be used for carrying and mounting the polishing workpiece, and the quality of the carrier film directly influences the polishing effect of the polishing workpiece.
FIG. 1 shows a schematic view of a polishing device with a conventional carrier film. The polishing device 1 includes a lower base plate 11, a carrier film 12, a polishing workpiece 13, an upper base plate 14, a polishing pad 15 and slurry 16. The carrier film 12 is adhered to the lower base plate 11 through an adhesive layer 17 and is used for carrying and mounting the polishing workpiece 13. The polishing pad 15 is mounted on the upper base plate 14.
The operation mode of the polishing device 1 is as follows. First, the polishing workpiece 13 is mounted on the carrier film 12, and then both the upper and lower base plates 14 and 11 are rotated and the upper base plate 14 is simultaneously moved downward, such that the polishing pad 15 contacts the surface of the polishing workpiece 13, and a polishing operation for the polishing workpiece 13 may be performed by continuously supplementing the slurry 16 and using the effect of the polishing pad 15.
FIG. 2 is a first type of the conventional carrier film. The material of the first type of the conventional carrier film is elastomer such as foamed polyurethane. The surface of the carrier film is polished to form a suede-like surface. The carrier film comprises only one substrate, and the bottom of the substrate is more solid than the upper part of the substrate. Since the thickness of the substrate is restricted, it can only provide a minor buffer effect. In a chemical mechanical polishing process, the rotated upper base plate move downward, and a down force occurs from the upper base plate through the polishing pad and is applied on the polishing workpiece. Consequently, the down force applied on the polishing workpiece fails to be conducted and released evenly, because the conventional carrier film cannot provide a proper buffer effect. Such an uneven force usually shoves the polishing workpiece and causes it to be cracked.
A second type of the conventional carrier film is developed and shown in FIG. 3. The carrier film comprises a surface substrate and at least one buffer substrate. The materials of the surface substrate and the buffer substrate are elastomer such as foamed polyurethane. The surface and buffer substrate are adhered with pressure sensitive adhesive (PSA). One embodiment of the pressure sensitive adhesive comprises a film comprising polyethylene terephthalate, for example, and has adhesive with a low fluidity on an upper side and a lower side of the film, such adhesive being known as dual-sided adhesive. The thickness of the adhesive is usually more than 20 μm. The adhesive on the upper side of the film is configured to couple to the surface substrate, and that on the lower side of the film is to couple to the buffer substrate. The surface of the carrier film is polished to form a suede-like surface. By applying the buffer substrate, the down force is conducted and released to a certain degree. However, because the hardness rates and contraction rates of the pressure sensitive adhesive, surface substrate and buffer substrate are different, the buffer effect is reduced thereby. Furthermore, the film of the pressure sensitive adhesive provides no buffer effect at all. Such factors also shove the polishing workpiece and cause it to be cracked when polishing.